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Refactor heapam.c adding heapgettup_initial_block function 

Here we adjust heapgettup() and heapgettup_pagemode() to move the code
that fetches the first block number to scan out into a helper function.
This removes some code duplication.

Author: Melanie Plageman
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/CAAKRu_bvkhka0CZQun28KTqhuUh5ZqY=_T8QEqZqOL02rpi2bw@mail.gmail.com
This commit is contained in:
David Rowley 2023-02-02 14:17:15 +13:00
parent 253432f426
commit fb1a59de0c
1 changed files with 104 additions and 123 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

227
src/backend/access/heap/heapam.c
View File

@ -483,6 +483,67 @@ heapgetpage(TableScanDesc sscan, BlockNumber block)
scan->rs_ntuples = ntup;
}
/*
* heapgettup_initial_block - return the first BlockNumber to scan
*
* Returns InvalidBlockNumber when there are no blocks to scan. This can
* occur with empty tables and in parallel scans when parallel workers get all
* of the pages before we can get a chance to get our first page.
*/
static BlockNumber
heapgettup_initial_block(HeapScanDesc scan, ScanDirection dir)
{
Assert(!scan->rs_inited);
/* When there are no pages to scan, return InvalidBlockNumber */
if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
return InvalidBlockNumber;
if (ScanDirectionIsForward(dir))
{
/* serial scan */
if (scan->rs_base.rs_parallel == NULL)
return scan->rs_startblock;
else
{
/* parallel scan */
table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
scan->rs_parallelworkerdata,
(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel);
/* may return InvalidBlockNumber if there are no more blocks */
return table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
scan->rs_parallelworkerdata,
(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel);
}
}
else
{
/* backward parallel scan not supported */
Assert(scan->rs_base.rs_parallel == NULL);
/*
* Disable reporting to syncscan logic in a backwards scan; it's not
* very likely anyone else is doing the same thing at the same time,
* and much more likely that we'll just bollix things for forward
* scanners.
*/
scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
/*
* Start from last page of the scan. Ensure we take into account
* rs_numblocks if it's been adjusted by heap_setscanlimits().
*/
if (scan->rs_numblocks != InvalidBlockNumber)
return (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
if (scan->rs_startblock > 0)
return scan->rs_startblock - 1;
return scan->rs_nblocks - 1;
}
}
/* ----------------
* heapgettup - fetch next heap tuple
*
@ -527,38 +588,19 @@ heapgettup(HeapScanDesc scan,
{
if (!scan->rs_inited)
{
block = heapgettup_initial_block(scan, dir);
/*
* return null immediately if relation is empty
* Check if we have reached the end of the scan already. This
* could happen if the table is empty or if the parallel workers
* have already finished the scan before we did anything ourselves
*/
if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
if (scan->rs_base.rs_parallel != NULL)
{
ParallelBlockTableScanDesc pbscan =
(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
ParallelBlockTableScanWorker pbscanwork =
scan->rs_parallelworkerdata;
table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
pbscanwork, pbscan);
block = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
pbscanwork, pbscan);
/* Other processes might have already finished the scan. */
if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
}
else
block = scan->rs_startblock; /* first page */
heapgetpage((TableScanDesc) scan, block);
lineoff = FirstOffsetNumber; /* first offnum */
scan->rs_inited = true;
@ -582,60 +624,40 @@ heapgettup(HeapScanDesc scan,
}
else
{
/* backward parallel scan not supported */
Assert(scan->rs_base.rs_parallel == NULL);
if (!scan->rs_inited)
{
block = heapgettup_initial_block(scan, dir);
/*
* return null immediately if relation is empty
* Check if we have reached the end of the scan already. This
* could happen if the table is empty.
*/
if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
/*
* Disable reporting to syncscan logic in a backwards scan; it's
* not very likely anyone else is doing the same thing at the same
* time, and much more likely that we'll just bollix things for
* forward scanners.
*/
scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
/*
* Start from last page of the scan. Ensure we take into account
* rs_numblocks if it's been adjusted by heap_setscanlimits().
*/
if (scan->rs_numblocks != InvalidBlockNumber)
block = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
else if (scan->rs_startblock > 0)
block = scan->rs_startblock - 1;
else
block = scan->rs_nblocks - 1;
heapgetpage((TableScanDesc) scan, block);
}
else
{
/* continue from previously returned page/tuple */
block = scan->rs_cblock; /* current page */
}
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
lines = PageGetMaxOffsetNumber(page);
if (!scan->rs_inited)
{
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
lines = PageGetMaxOffsetNumber(page);
lineoff = lines; /* final offnum */
scan->rs_inited = true;
}
else
{
/* continue from previously returned page/tuple */
block = scan->rs_cblock; /* current page */
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
lines = PageGetMaxOffsetNumber(page);
/*
* The previous returned tuple may have been vacuumed since the
* previous scan when we use a non-MVCC snapshot, so we must
@ -837,38 +859,19 @@ heapgettup_pagemode(HeapScanDesc scan,
{
if (!scan->rs_inited)
{
block = heapgettup_initial_block(scan, dir);
/*
* return null immediately if relation is empty
* Check if we have reached the end of the scan already. This
* could happen if the table is empty or if the parallel workers
* have already finished the scan before we did anything ourselves
*/
if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
if (scan->rs_base.rs_parallel != NULL)
{
ParallelBlockTableScanDesc pbscan =
(ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
ParallelBlockTableScanWorker pbscanwork =
scan->rs_parallelworkerdata;
table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
pbscanwork, pbscan);
block = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
pbscanwork, pbscan);
/* Other processes might have already finished the scan. */
if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
}
else
block = scan->rs_startblock; /* first page */
heapgetpage((TableScanDesc) scan, block);
lineindex = 0;
scan->rs_inited = true;
@ -889,58 +892,36 @@ heapgettup_pagemode(HeapScanDesc scan,
}
else
{
/* backward parallel scan not supported */
Assert(scan->rs_base.rs_parallel == NULL);
if (!scan->rs_inited)
{
block = heapgettup_initial_block(scan, dir);
/*
* return null immediately if relation is empty
* Check if we have reached the end of the scan already. This
* could happen if the table is empty.
*/
if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
/*
* Disable reporting to syncscan logic in a backwards scan; it's
* not very likely anyone else is doing the same thing at the same
* time, and much more likely that we'll just bollix things for
* forward scanners.
*/
scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
/*
* Start from last page of the scan. Ensure we take into account
* rs_numblocks if it's been adjusted by heap_setscanlimits().
*/
if (scan->rs_numblocks != InvalidBlockNumber)
block = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
else if (scan->rs_startblock > 0)
block = scan->rs_startblock - 1;
else
block = scan->rs_nblocks - 1;
heapgetpage((TableScanDesc) scan, block);
}
else
{
/* continue from previously returned page/tuple */
block = scan->rs_cblock; /* current page */
}
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
lines = scan->rs_ntuples;
if (!scan->rs_inited)
{
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
lines = scan->rs_ntuples;
lineindex = lines - 1;
scan->rs_inited = true;
}
else
{
/* continue from previously returned page/tuple */
block = scan->rs_cblock; /* current page */
page = BufferGetPage(scan->rs_cbuf);
TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
lines = scan->rs_ntuples;
lineindex = scan->rs_cindex - 1;
}
/* block and lineindex now reference the previous visible tid */